Gain-control arrangement



Oct. 21, 1 947. J, A, HANSEN Erm., 2,429,513

l GAN-CONTROL ARRANGEMENT Filed Feb. 11, 1944 2 sheets-sheet 2 PatentedOct. 21, 1947 GAIN -CONTBOL ABRANGEMENT John A. Hansen and Bernard D.Loughlin, Bayside, N. Y., assignors. by mesne assignments, to

Hazeltin poration of IllinoisV e Research, Inc.. Chicago, Ill.. a cor-Application February 11, 1944, Serial No. 521,926

11 Claims. (CL Z50-20) The present invention is directed to a gain-'control arrangement for a receiver for translating a receivedpulse-modulated signal having a pulse-repetition frequency which mayvary over a wide frequency range. The invention is subject to a varietyof applications but is especially suited for use in a wave-signaltransponder system and will be particularly described in thatconnection. As used throughout this specification, the term wave-signaltranspondor system" is intended to designate a wave-signal translatingsystem including a receiver and a transmitter arranged to transmit areply signal in response to a received interrogating signal, each suchsignal preferably comprising a pulse-modulated radiant-energy signal.Generally the interrogating and reply signals have carrier frequencieswhich are equal, or nearly so, and pulse-repetition frequencies whichare either identical or integrally related. 4

In one prior transpondor arrangement, the receiver is of thesuperregenerative type having a linear mode of operation and thetransmitter is triggered, or set into operation, under the control ofthe receiver through an amplitude-selective circuit. Optimum sensitivityof such an arrangement is obtained by adjusting the receiver gain to acompromise value between that which is required for maximum receiversensitivity and that which is necessary to assure freedom fromtriggering the transmitter on the quiescent signal components of thereceiver. These quiescent signal components comprise the noise signaloutput obtained during intervals when no desired signal is beingreceived. In general, the quiescent signal components have a relativelylow amplitude as determined by the noise signals present in the receivercircuit, but their amplitude varies with variations of the operatingpotentials, tube characteristics and similar factors. In order tomaintain freedom from triggering the transmitter on the quiescent signalcomponents, it is customary to embody a gain-control orgain-stabilization arrangement in the receiver for controlling thereceiver gain to maintain the amplitude level of such signal componentsat that value required for optimum sensitivity.

Prior gain-control arrangements generally include a system whichrectifles a selected portion of the quiescent signal output of thereceiver to derive a gain-control voltage In one such arrangement, thatcomponent of the quiescent signal which has a frequency corresponding tothe quench frequency of the receiver is utilized in developing thedesired gain-control voltage. Ar-

rangements of this type are able to maintain optimum sensitivity so longas the translated pulsemodulated signals have low pulse-repetitionfrequencies. As the repetition frequency increases, however, there is atendency for the gain-control circuit undesirably to reduce the receiversensitivity. This results from the fact that each pulse of the receivedinterrogating signal causes the signal outputof the receiver to have anincreased amplitude and, at high repetition frequencies, the effect isto increase the average level of the signal input to the gain-controlarrangement. As a consequence. the derived control voltage varies in asense which tends to reduce the receiver gain and sensitivityaccordingly. This desensitizing effect is most pronounced where thetransmitted reply signal makes its way into the receiver circuit, as forexample in transpondor systems where the receiver and transmitter havecommon circuit elements providing a feed-back path into the receiver. Insuch a case, the transmitted reply signal, which has an exceedingly highenergy content and signal components falling within the pass band of thegain-control system, greatly 1ncreases the level oi the signal appliedto the gaincontrol system at high repetition frequencies.

Compensating circuits have been proposed for reducing this effect. ,Oneform of compensating circuit that has been utilized consists of .adifferentiating circuit for eliminating some of the energy content ofthe high-amplitude signal components that are applied to thegain-control system each time the transmitter operates. Othercompensating circuits decrease the gain of one or more ampliers includedin the gain-control system during intervals when the transmitter isoperating. Such compensating circuits, however, are eEective to maintainthe desired receiver sensitivity for only a limited range ofpulse-repetition frequencies.

It is an object of the invention, therefore, to provide an improvedgain-control arrangement for a receiver for translating pulse-modulatedsignais and which avoids one or more of the aforementioned limitationsof prior art arrangements.

It is another object of the invention to provide an improvedgain-control arrangement for a receiver for translating a receivedpulse-modulated signal having a repetition frequency which may vary overa wide frequency range.

In accordance with the invention, a gain-control arrangement for a.receiver for translating a received pulse-modulated signal having arepetition frequency which may vary over a wide frequency rangecomprises means for deriving from that initiates the oscillations insucceeding quench cycles. For the no-signal condition underconsideration. the exciting signal comprises the low-amplitude noisesignals present in the receiver circuit so that the oscillationsproduced in successive quench cycles have a correspondingly smallamplitude value.

The generated oscillations are detected by detector 2|, producing acrossresistor 23 a low-amplitude periodic-signal voltage which has beenreferred to above as the quiescent signal of the receiver. This signalhas a frequency component corresponding to the frequency of the quenchvoltage and includes components harmonically related to the quenchfrequency as Y well-as components corresponding to the noise signals ofthe receiver circuit. The quiescent signal is translated through pulseamplier 40 and applied to cathode follower 43, producing across itscathode impedance 44 a control voltage. The control voltage so developedis applied to the control electrode of transmitter tube 30 but, for theassumed condition of optimum sensitivity, has insumcient magnitude toovercome the bias voltage applied to the transmitter by bias resistor33. Consequently, the quiescent signal components derived from thereceiver have no effect on the transmitter which remains blocked.

Let it be assumed now that an aircraft desiring direction-findinginformation from the transpondor transmits thereto an interrogatingsignal having a wave form as represented by curve a of Fig. 2. Theinterrogating signal is a .pulse-modulated radio-frequency signal havinga carrier frequency substantially equal to the operating frequency ofthe receiver and a predetermined pulse-repetition frequency. In general,this signal will have a high intensity with reference to the noisesignals in the receiver so that the oscillations generated in eachquench cycle occurring within the interval of a received pulse have arelatively high amplitude. If the operation of the transmitter beneglected, the detected output signal of the receiver obtained inresponse to the received interrogating signal may have the wave form ofcurve b of Fig. 2. This output signal has low-amplitude quiescent signalcomponents Sq occurring at the quench frequency and high-amplitudecomponents Sidetermined by the pulse modulation of the received signaland occurring at a frequency which corresponds to the pulse-repetitionfrequency thereof. The high-amplitude components Sr. after translationthrough pulse amplifler 40 and cathode follower 43, produce acrosscathode impedance 44 a control voltage of sufcient magnitude to overcomethe blocking potential normally applied to tube 30 and initiateoscillations in the transmitter.

The oscillations generated in the transmitter are also applied todetector 2l through the common tuned circuit and are fed back to theinput circuit of tube 30 through a regenerative circuit including diodedetector 2l, pulse amplifier 40 and cathode follower 43, which augmentsthe inherent feedback of the transmitting oscillator. For this reason,the generated oscillations of the transmitter reach saturation amplitudevalue early in the transmitter cycle, causing the transmitted pulse tohave full power irrespective of the power of the interrogating signal.As the oscillations of tube 30 continue, condenser 34 included in itscathode circuit becomes charged. raising the cathode potential thereofand tending to terminate transmission. The value of condenser 34 is sochosen that the transmitted pulse has a predetermined pulse durationwhich may be equal to that of the pulse duration of the receivedinterrogating signal. Condenser 34 in discharging through resistor 33determines the recovery time of the transmitter. The wave form oi thetransmitted reply signal will be substantially as represented in curve aof Fig. 2. The reply comprises a pulse-modulated radio-frequency signalhaving substantially the same carrier frequency and modulation as theinterrogating signal but being. in the usual case. of very much greaterintensity.

Noting that the transmitted signal is also applied to detector 2|, itwill be seen that as far as thesignaloutput of the detector isconcerned,V

the transmitted signal is equivalent to and may be considered as areceived signal. Therefore, when the transmitter operation is taken intoconsideration. the output signal obtained from detector 2|, in responseto an interrogating signal, may be as represented by curve c of Fig. 2,in which the high-amplitude signal components St represent the detectedtransmitted pulses. These components have a much greater relativeintensity than the components Sr of curve b than can be convenientlyrepresented in the drawing. Also, for convenience of representation, thehighamplitude signal components Sr derived by detector 2l in response toa received pulse for triggering the transmitter are represented asmerged into the transmitted pulse. This representation is substantiallyaccurate since the transmitter is triggered into operation by theleading edge of the triggering pulse.

Reference is now made to unit 50 provided in the transpondor system inaccordance with the teaching of the present invention to control thegain characteristic of the receiver. This unit is coupled tol detector2l through pulse amplifier 40 and comprises means for deriving from theoutput signal of the receiver a second signal. Unit 50 includesamplitude-responsive means responsive to the high-amplitude componentsof the receiver output signal for eliminating from the derived secondsignal an energy content which is at least substantially equal to thatof the energy content contributed by such high-amplitude components tothe second signal. More speciilcally. unit 50 includes a vacuum-tubesignal repeater or ampliiieril having a self-bias resistor 52 andcoupled to the output circuit of pulse amplier 40 by means of acondenser 53 and grid resistor 54. The operating potentials applied totube 5I and the values of bias resistor 52 and condenser 53 are sochosen that high-amplitude signal components of positive polarityapplied to the input circuit of the tube produce grid current limitingin which the control electrode and cathode of the tube function,respectively, as anode and cathode elements of a diode rectifier. Gridresistor 54 is selected to have a high value of impedance for a purposeto be described presently. A second amplifier 55 is coupled to theoutput circuit of amplier 5| and includes in its input circuit acondenser-resistor combination, comprising a condenser 56 and a resistor5l, arranged to form a conventional differentiating circuit. The outputcircuit of amplifier 55 includes the primary circuit of a double-tunedtransformer 58 damped by a resistor 59. Transformer 58 is tuned to thequench frequency of the receiver, thereby to derive in unit 50 theabove-mentioned second signal.

Unit 50 also includes means, comprising a di- 7 ode rectifier 60, forrectifylng this second signal to derive a control effect which isutilized to control the gain of the receiver. The load circuit ofrectifier 60 includes the tuned secondary winding of transformer 58, aresistor 6| and a by-pass condenser 62. The rectified signal voltageproduced across resistor 6| is applied with negative polarity to theinput circuit of a directy current amplifier -63 through a low-passfilter provided by series resistors 64 and 65 and a shunt condenser 66.Amplifier 63 is a conventional amplifier except that its load impedance61 is located in the cathode circuit. A gain-control'voltage ofadjustable magnitude is obtained from a voltage tap 68 of impedance 61and is applied by way of a resistor 69 to the control electrode ofreceiver tube I 0.

In considering the operation of the described control arrangement, itwill be assumed initially that no signals are being intercepted byantenna system 46. For the assumed conditions, the lowamplitudequiescent signal output of the receiver derived in the circuit ofdetector 2| as described above is amplied in pulse amplifier 40 andapplied with positive polarity to the input circuit of unit 50. Thissignal is translated through ampliiiers 5| and 55 and a second signal isderived therefrom in the output circuit of amplifier 55, this secondsignal comprising the quench-frequency component of the quiescent signaloutput of the receiver. The derived second signal is rectified by dioderectifier 60, producing across resistor 6| a signal voltage which isapplied with negative polarity to direct current amplifier 63. The inputcircuit of amplifier 63 is such that the direct current component of therectifier output signal is applied directly between its controlelectrode and cathode, while the alternating current components thereofare effectively applied between the control electrode of'tube 63 andground. Therefore, tube 63 is a cathode follower with reference toalternating current signals so that the gain-control voltage developedacross impedance 6l and applied to the control electrode of receivertube I0 is substantially a pure direct current voltage. The magnitude ofthis gain-control voltage is directly proportional to the amplitude ofthe quiescent signal output of the receiver. The circuit parameters andoperating potentials of unit 50 are so selected that under normalconditions of operation this control voltage has such magnitude as toestablish optimum sensitivity of the receiver circuit. If a change inthe operating conditions of the receiver causes the amplitude of thequiescent signal output to be increased, the negative-polarity signalvoltage applied to amplier 63 is increasedproportionately, renderingtube 63 less conductive. The magnitude of the gain-control voltagedeveloped across impedance 6l is decreased accordingly, reducing thegain of the re'- ceiver and restoring the amplitude of the quiescentsignal output to that value which is required for optimum sensitivity.Conversely, a decrease in the amplitude of the quiescent signalcomponents produces an increase in the magnitude of the gain-controlpotential applied to tube |0, whereby the receiver gain is increased tomaintain optimum sensitivity.

In considering the operation of the gain control arrangement duringintervals when the transpondor system replies to a receivedinterrogating. lsignal, reference is made to the curves of Fig..3.

The output signal of detector 2 I during such intervals is appliedthrough amplifier 40 to the input circuit of unit 50 with a wave form asrepre- 8 sented by curve d. 'I'his signal includes the lowamplitudequiescent signal components Sq of the receiver and the high-amplitudecomponents St which correspond to the pulses of the transmitted replysignal. The high-amplitude components St which are effective to causethe gain-control arrangements of the prior art undesirably to reduce thesensitivity of the receiver as mentioned above, are effectivelysuppressed in unit 50 to a contrplled degree in order that the receivermay have a desired sensitivity-pulse repetition-frequencycharacteristic. The manner in which this is accomplished is illustratedby the remaining curves of Fig. 3.

The high-amplitude signal components Sr are rectified' in the inputcircuit of amplifier 5| thereby charging condenser 53. The charge oncondenser 53, Which can be dissipated only through the high-impedanceresistor 54, applies a transient signal voltage of negative polarity tothe control electrode of amplifier 5| which decays in accordance with anexponential function determined by the time constant of condenser 53 andthe resistor 54. The resulting signal voltage established on the controlelectrode of amplifier 5| is represented by the curve `e of Fig. 3.Assuming amplifier 5| to have a cut-olf level as indicated bybroken-line curve f, it will be seen that the high-amplitude componentsSt of the signal output from detector 2| are effective periodically toblock amplier 5| for intervals t which are short with reference to theperiod corresponding to the pulse-repetition frequency of thel receivedand transmitted signals. The effect of such blocking is to eliminatefrom the signal translated by amplier 5| those quiescent signalcomponents Sq which occur during the intervals t. Therefore, the signalproduced in the output circuit of amplier 5| has a Wave form representedby curve g.

The energy content of the high-amplitude components included in thissignal is materially reduced by the differentiating circuit associatedwith amplifier 55, establishing on the control electrode thereof asignal voltage represented by curve h. The quench-frequency component ofthis signal is selected in the output circuit of amplier 55, asdescribed a-bove, to comprise a second signal which is rectified inrectilier 60 to derive a gain-control voltage. Where it is desired tomaintain substantially optimum sensitivity of the receiver withvariations of the pulse-repetition frequency of the interrogatin'g andreply signals, unit 50 is to be adjusted in the following manner. Theblocking arrangement associated with amplier 5| and the differentiatingcircuit coupled to amplifier 55 are adjusted to eliminate from theabove-mentioned second signal a -portion of the energy contentcontributed thereto by the high-amplitude components St and a portion ofthe energy content contributed to the second signal by the quiescentsignal components Sq which is substantially equal to the remainingportion of the energy content contributed to the second signal by thehigh-amplitude components Expressed diiierently, these circuitarrangements are to be so adjusted that the second signal, derived inthe output circuit of amplifier 55, has substantially only the energycontent contributed thereto by the quiescent signal components Sq of thereceiver even during intervals when the transpondor system is replyingto a received interrogatunit 50. Curve k indicates a substantially iiatsensitivity characteristic obtained by adjusting unit 50 in the mannerrecited above. By increasing the discharge time constant of condenser53, a greater portion of the energy content contributed to the secondsignal by the quiescent signal components is removed, resulting in therising characteristic of curve l. On the other hand. a reduction of thistime-constant may produce the drooping characteristic of curve m.

It will be understood that the quench voltage utilized to providesuperregeneration may have a rectangular or other suitable wave forminstead of the described sinusoidal wave form. Also, control arrangement50 need not necessarily select the quench-frequency component of thereceiver quiescent signal output as the abovedescribed second signal forrectication by rectifier 60. If desired, the selector circuits of unit50 may be arranged to select, as the second signal, a portion of thenoise-signal components of the quiescent signal output.

In the described transpondor system' the receiver and transmitter sharea common frequency-determining circuit. It will be understood that theinvention is equally applicable to other transpondor arrangements as,for example, one wherein a single regenerative oscillatory circuit isutilized for both receiving and transmitting. Likewise, the inventionmay be utilized in a transpondor system having completely independentreceiver and transmitter portions but including some arrangement, suchas an antenna system, through which the transmitted signal may be fedback to the receiver.

It will also be understood that the invention may be applied to asuperheterodyne, as distinguished from a superregenerative, receiver. Insuch a case the gain-control system of the invention likewise comprisesan arrangement for deriving a control voltage from the noise signaloutput of the receiver which is utilized to maintain the receiver noisesignal at a predetermined level.

While there has been described what is at present considered to be thepreferred embodimeritl of this invention, it will be obvious to thoseskilled in the art that various changes and modifications may be madetherein without departing from the invention, and it is, therefore,aimed in the appended claims to cover all such changes and modificationsas fall Within the true spirit and scope of the invention.

What is claimed is:

1. A gain-control arrangement for a receiver for translating a receivedpulse-modulated signalhaving a repetition frequency which may vary overa wide frequency range comprising, means for deriving from said receiveran output signal having low-amplitude quiescent signal components andhigh-amplitude components determined bv the pulse modulation of saidreceived signal, means for translating said output signal to produce asecond signal and including means responsive to said high-amplitudecomponents for effectively eliminating from said output signal duringthe translation thereof an energy content which is at leastsubstantially equal to all of the energy content contributed by saidhigh-amplitude components to said output signal, means for rectifyingsaid output signal to derive a control eiiect, and means for utilizingsaid control effect to control the gain of said receiver.

2. A gain-control arrangement for a super- I regenerative receiverhaving a given quench frequency and for translating a received pulsel0modulated signal having a repetition frequency which may vary over aWide frequency range comprising, means for deriving from said receiveran output signal having low-amplitude quiescent signal componentsoccurring at said quench frequency and high-amplitude signal components`determined by the pulse modulation of said received signal, means fortranslating said output signal to produce a second signal and includingmeans responsive to said high-amplitude components for effectivelyeliminating from said output signal during the translation thereof anenergy content which is at least substantially equal to all of theenergy content contributed by said high-amplitude components to saidoutput signal, means for rectifying said second signal to derive acontrol effect, and means for utilizing said control effect to controlthe gain of said receiver.

3. A gain-control arrangement for a superregenerative receiver having agiven quench frequency and for translating a received pulse-modulatedsignal having a repetition frequency which may vary over a widefrequency range comprising, means for deriving from said receiver anoutput signal having low-amplitude quiescent signal components occurringat said quench frequency and high-amplitude signal components determinedby and occurring at the repetition frequency of the puise modulation ofsaid received signal, means for translating said output signal toproduce a second signal and including means responsive to saidhigh-amplitude components for eectively eliminatingfrom said outputsignal during the translation thereof an energy content which is atleast substantially equal to all of the energy content contributed bysaid high-amplitude components to said output signal, means forrectifying said second signal to derive a control eifect, and means forutilizing said control effect to control the gain of said receiver.

4. A gain-control arrangement for a receiver for translating a receivedpulse-modulated signal having a repetition frequency which may vary overa wide frequency range comprising, means for deriving from said receiveran output signal having low-amplitude quiescent signal components andhigh-amplitude components determined by the pulse modulation of saidreceived signal, means for translating said output signal to produce asecond signal and including means responsive to said high-amplitudecomponents for effectively eliminating from said output signal duringthe translation thereof an energy content which is substantially equalto al1 of the energy content contributed by said high-amplitudecomponents to said output signal, means for rectifying said secondsignal to derive a control effect, and means for utilizing said controleffect to control the gain of said receiver.

5. A gain-control arrangement for a receiver for translating a receivedpulse-modulated signal having a repetition frequency which may vary overa wide frequency range comprising, means for deriving from said receiveran output signal having low-amplitude quiescent signal components andhigh-amplitude components determined by the pulse modulation of saidreceived signal, means for translating said output signal to produce asecond signal and including amplitude-responsive means responsive tosaid highamplitude components for effectively eliminating from saidoutput signal during the translation thereof an energy content which isat least substantially equal to all of the energy content contributed bysaid high-amplitudev components to said output signal, means forrectifying said second signal to derive a control effect, and means forutilizing said control effect to control the gain of said receiver.

6. A gain-control arrangement for a receiver for translating a receivedpulse-modulated signal having a repetition frequency which may vary overa. wide frequency range comprising, means for deriving from saidreceiver an output signal having low-amplitude quiescent signalcomponents and high-amplitude components determined by the pulsemodulation of said received signal, means for translating said outputsignal to produce a second signal and including means responsive to saidhigh-amplitude components of said output signal for effectivelyeliminating from said output signal during the translation thereof aportion of the energy content contributed thereto by said high-amplitudecomponents and a portion of the energy content contributed to saidoutput signal by said quiescent signal components which is at leastsubstantially equal to the remaining portion of said energy contentcontributed to said output signal by said highamplitude components,means for rectifying said second signal to derive a control effect, andmeans for utilizing said control eilect to control the gain of saidreceiver.

7. A gain-control arrangement for a receiver for translating a receivedpulse-modulated signal having a repetition frequency which may vary overa wide frequency range comprising, means for deriving from said receiveran output signal having low-amplitude quiescent signal components andhigh-amplitude components determined by the pulse modulation of saidreceived signal, means for translating said output signal to produce asecond signal and including means responsive to said high-amplitudecomponents of said output signal for effectively eliminating from saidoutput signal during the translation thereof a portion of the energycontent contributed thereto by said high-amplitude components and meansresponsive to said high-amplitude components of said output signal foreliminating from said output signal during said translation a portion ofthe energy content contributed thereto by said quiescent signalcomponents which is at least substantially equal to the remainingportion of said energy content contributed to said output signal by saidhigh-amplitude components, means for rectifying said second signal toderive a control effect, and means for utilizing said control eiect tocontrol the gain of said receiver.

8. A gain-control arrangement for a receiver for translating a receivedpulse-modulated signal having a repetition frequency which may vary overa wide frequency range comprising, means for deriving from said receiveran output signal having low-amplitude quiescent signal components andhigh-amplitude components determined by the pulse modulation of saidreceived signal, means for translating said output signal to produce asecond signal and including means responsive to said high-amplitudecomponents of said output signal for effectively eliminating from saidoutput signal during the translation thereof a portion of the energycontent contributed thereto by said high-amplitude components and asignal repeater having means responsive to said high-amplitude componntsof said output signal for periodically blocking said repeater toeliminate from said output signal during said translation a portion ofthe energy content contributed thereto by said quiescent signalcomponents which is at least substantially equal to the remainingportion of said energy content contributed to said output signal by saidhigh-amplitude components, means for rectifying said second signal toderive a control eii'ect, and means fory tilizing said control eil'ectto control the gain of' said receiver.

9. A gain-control arrangement for a receiver for translating a receivedpulse-modulated signal having a repetition frequency which may vary overa wide frequency range comprising, means for deriving from said receiveran output signal having low-amplitude quiescent signal components andhigh-amplitude components determined by the pulse modulation of saidreceived signal, means for translating said output signal to produce asecond signal and including means responsive to said high-amplitudecomponents of said output signal for eil'ectively eliminating from saidoutput signal during the translation thereof a, portion of the energycontent contributed thereto by said high-amplitude components and avacuum-tube signal repeater having means responsive to saidhigh-amplitude components of said output signal for periodicallyblocking said repeater to eliminate from said output signal during saidtranslation a portion of the energy content contributed thereto by saidquiescent signal components which is at least substantially equal to theremaining portion of said energy content' contributed to said outputsignal by said high-amplitude components, means for rectifying saidsecond signal to derive a control eiect, and means for utilizing saidcontrol effect to control the gain oi' said receiver.

10. A gain-control arrangement for a receiver for translating a receivedpulse-modulated signal having a repetition frequency which may vary overa wide frequency range comprising, means for deriving from said receiveran output signal having low-amplitude quiescent signal components andhigh-amplitude components determined by the pulse modulation of saidreceived signal, means for translating said output signal to produce asecond signal, said last-named means including means responsive to saidhigh-amplitudev components of said output signal for eil'ectivelyeliminating from said output signal during the translation thereof aportion of the energy content contributed thereto by said high-amplitudecomponents and a signal repeater having means responsive to saidhigh-amplitude components of said output signal for periodicallyblocking said repeater for intervals which are short with reference tothe period corresponding to said repetition frequency of said receivedsignal to eliminate from said output signal during said translation aportion of the energy content contributed thereto by said quiescentsignal components which is at least substantially equal to the remainingportion of said energy content contributed to said output signal by saidhighamplitude components, means for rectifying said second signal toderive a control eect, and means for utilizing said control eil'ect tocontrol the gain of said receiver.

11. A gain-control arrangement for a wavesignal transpondor system whichis responsive to a received pulse-modulated signal having apredetermined carrier frequency and a repetition frequency which mayvary over a wide frequency range for transmitting a, pulse-modulatedreply signal having a carrier frequency substantially equal to that ofsaid received signal and a repeamplitude components tition frequencyrelated to that. of said receivedl signal comprising, means tor derivingfrom said transponder system an output signal having lowamplitudequiescent signal components and highdetermined by the pulse modulationof said reply signal, means for translating said output signal toproduce a, second signal and including means responsive to saidhighamplitude components for effectively eliminating from said outputsignal during the translation thereof an energy content which is atleast substantially equal to all of the energy content contributed bysaid high-amplitude components to said output signal, means forrectifying said second signal to derive a control effect, and means forutilizing said' control eiect to control the gain of said transpondorsystem.

' JOHN A. HANSEN.

BERNARD D. LOUGHLIN.

REFERENCES crrnn The following references are of record in the ile ofthis patent:

UNITED STATES PATENTS Number Oct. 21, 1947,' B. D. I OUGHLINRADIANT-ENERGY SIGNAL DIRECTION FINDER Filed sept. 2o, 1943 4sheets-sheet 1 I I I I I I I I I I I I I I I I I I I I I I I I I I I I II I I I l I I I I l I I .I

O II mojmoo mov mojmom o 5.2.55. o @z zzoo INVENTOR BERNAR D. LOUGHLIN AORNEY

